Nozzles are employed in a wide variety of applications to direct flowable materials such as particulate solids, liquids or gases in a desired flow path. In many applications, nozzles function to accelerate the flowable material supplied from a source at constant pressure and flow rate. Typically, the flowable material is pumped from the source through a supply line which is connected to a nozzle having a discharge passageway of smaller diameter than the supply line so that at constant pressure and flow rate the velocity of the flowable material ejected from the discharge orifice of the nozzle is much greater than its velocity through the supply line.
In nozzles of the type described above, a "transition area" is formed between the supply line and discharge orifice of the nozzle in which the diameter or cross sectional area of the flow path of the flowable material decreases For example, one type of "transition area" employed in the prior art resembles a venturi tube in which the flow path of the flowable material uniformly tapers in a radially inward direction from the larger diameter supply line to the much smaller diameter discharge orifice in the nozzle. This uniform taper in the transition area of the flow path between the supply line and nozzle discharge orifice is intended to create laminar flow of the flowable material as it moves into the nozzle so as to reduce turbulence and drag losses and thus improve the nozzle "efficiency". The term "efficiency" as used herein refers to the actual velocity or flow rate of the flowable material ejected from the discharge orifice of a nozzle as a percentage of the ideal, i.e., theoretical velocity or flow rate, which would be obtained if there were no losses due to drag or turbulence.
Although it has been found that nozzle efficiency can be increased by providing a smoothly tapering transition area, the efficiency of such nozzles is not optimum. Eddies and other turbulent flow of the flowable material are created along the walls of the tapered transition area which disrupts the flow pattern of the flowable material. Depending upon the viscosity of the flowable material, such turbulence creates drag and reduces the actual velocity or flow rate of the flowable material through the nozzle as compared to its theoretical velocity. In applications where the velocity or flow rate of the flowable material discharged from the nozzle is critical, such losses in the transition area leading to the discharge orifice of the nozzle may require the use of a larger pump, and/or an increased flow rate, in order to obtain the desired discharge velocity.